September 20, 2013

Researchers Identify Ray Species Used For Their Filters In Asian Medical Trade

A newly published study led by researchers at the University of Washington has identified the anatomical differences between the different filters of various marine rays. Study researchers said their findings could be used to assess the species of ray filters being sold in Asian apothecary shops and to create new and improved manufacturing filters.

The Washington researchers said they have found enough signature markers to be able to identify the giant manta ray and eight of the devil rays based solely on an examination of the part from inside their mouth that has been cut out, dried and up for sale as a liver detoxifier.

“There is no historical or traditional medical use of these filters and there’s no scientific evidence they will help your liver filter out toxins,” said Misty Paig-Tran, who worked on the study while earning her doctorate in biology at the UW. “Still there are thousands of these ray filters in the markets, especially in Indonesia.”

Paig-Tran said now that they are able to identify which species are being killed for their filters – protection measures for these animals are a much easier proposition.

“You could take this paper to a market and tell which species the filters came from, and that would give you an idea of the number of each species being hunted,” she said.

A ray’s filter is essentially plates of tissue that share the fish’s gill arches with respiratory organs that extract oxygen from the water. Paig-Tran said that devil rays might pass 4 gallons a second or 240 gallons a minute through their gill arches.

The new study, which was published in the September edition of the Journal of Morphology, was based on specimens borrowed from museums and video recordings of rays and filter-feeding whale sharks near the Yucatan Peninsula, Mexico.

“Whale sharks are incredibly docile and don’t mind you in front of them, filming into their mouths. So long as you’re a fast swimmer, you’re OK,” Paig-Tran said.

“Mantas are more difficult,” she added. "Mantas have one of the largest brain-to-body ratio of any of the fishes. They are highly intelligent, they don’t like to be disturbed and they’re highly maneuverable.”

Seen feasting on plankton-rich upwells in tropical and subtropical ocean waters, not much is known about these rays’ habits. Paig-Tran said she placed satellite tags on a few of the rays to track their movements.

“Knowing their specific prey and if they are following blooms of particular plankton would be a way for us to remotely detect places where we might find these rays,” Paig-Tran said. “Then we could learn more about their basic biology, where they are going, where they mate, where are they [sic] producing their young.”

The study researchers also noted that the rays use cross-flow filtering, a type of filtering often seen in US manufacturing. However, artificial cross-flow filters eventually clog, while the filters of rays don’t. If they did, rays would have been extinct long ago.

“There is no filter in the manufacturing realm like the ones these rays use,” said co-author Adam Summers, a UW professor of biology.

--

Image Below: Water flows through the 40-inch (1 meter) wide mouth of a giant manta and over the ray’s gill arches, the white triangular parts running across the bottom and top of its mouth, five on each side. Its filters, too small to see at this distance, are located in the black portions in between. Credit: S Kajiura/Florida Atlantic U